Peter Calthorpe codified the concept of Transit-Oriented Development (TOD) in the late 1980's and, while others had promoted similar concepts and contributed to the design, TOD became a fixture of modern planning when Calthorpe published The New American Metropolis in 1993. TOD has been defined generally as a mixed-use community that encourages people to live near transit services and to decrease their dependence on driving. Calthorpe saw it as a neo-traditional guide to sustainable community design. Beyond its definition of built form, it was also a community design theory that promised to address a myriad of social issues. Calthorpe, a student of the environmental sustainability movement, developed TOD to address the ecology of communities. He also saw TOD as an easily comprehensible solution for regional growth. It also met the need of transit agencies for alternative revenue sources. And it was a natural evolutionary next-step from many familiar community design precedents. In its most bold promise, TOD was to help redefine the American Dream. As later TOD analysts explained, These Transit-oriented developments have the potential to provide residents with improved quality of life and reduced household transportation expense while providing the region with stable mixed-income neighborhoods that reduce environmental impacts and provide real alternatives to traffic congestion. This paper looks at the development of the TOD vision from multiple perspectives. First, the paper looks at a long history of transit served real estate development. Second, it evaluates TOD's position in a long history of social and urban theory. Lastly, it tracks Calthorpe's TOD concept through his lifetime of work up to the publication of The New American Metropolis. This paper is meant to serve as a foundation for further work that will seek to define the term TOD in its many uses across the fields of planning, design, transportation, and policy.